1. Field of the Invention
The present invention concerns the field of synchronous telecommunication networks such as SDH or SONET telecommunication networks and in particular it concerns protection architectures of SDH/SONET networks. Still more in particular, it concerns the optimization of information of the K-bytes.
2. Description of the Prior Art
As far as for example SDH frames are concerned, it is known from the ITU-T Recommendation G.707 that they are formed by structures which are nested at several synchronous multiplex layers whose basic components are called Synchronous Transport Modules level N (STM-N, N=1, . . . ) indicating the bit rate (for instance, STM-1 155 Mb/s, STM-16 2488 Mb/s). Each STM-N module comprises a header portion termed Section Overhead (SOH), containing management and synchronization auxiliary information, and a subsequent portion termed Information Payload containing the informative part.
The information of the SOH section is classified into Regeneration Section Overhead (RSOH) and Multiplex Section Overhead (MSOH) which passes through the regenerators in a transparent manner. In particular, in the MSOH section there is a plurality of bytes located at very definite standardized positions and bytes reserved for purposes to be defined and standardized.
As defined by ITU-T Recommendation G.841, the Automatic Protection Switching (briefly, APS) protocol of a telecommunication ring is carried on two special bytes, the so-called K1 and K2 bytes, of the MSOH section. In particular, the same ITU-T Recommendation G.841 provides that, as far as the K1 byte is concerned (see FIG. 3), its first four bits (bits aK11, aK12, aK13, aKl4) carry bridge request codes (codes requesting transmitting identical traffic over protection and working channels) whereas the subsequent four bits (bits aK15, aK16, aK17, aK18) carry identifications (IDs) of the destination node for the bridge request code indicated in the first four bits. The function of the byte K2 (see again FIG. 3) is as follows: the first four bits (bits aK21, aK22, aK23, aK24) carry source node identification; bits aK26, aK27, aK28, define the status of the node whereas the fifth bit (aK25) represents a path length code (0=short path, 1=long path).
For example, as far as the 2 fiber, 4 fiber and transoceanic MS-SPRING protections are concerned, the problem of increasing the number of nodes manageable by the protection arises. Since at present the available bits for the IDentification (ID) of the source (aK21, aK22, aK23, aK24) or destination (aK15, aK16, aK17, aK18) nodes are only four, the existing telecommunication rings cannot have more than sixteen nodes. This obviously represents a high limitation in the development of communications networks.
Another problem related to the K1 and K2 bytes is that, when they change, there is an interrupt from the ASIC to the microprocessor for each changed byte (hence one or, at the most, two). In any case it is necessary to manage the temporality of the events to fully manage the information contained in the K1 and K2 bytes.